Body coated with cubic boron nitride and method for manufacturing the same

ABSTRACT

A body coated with cubic boron nitride is disclosed which includes a base material, a first interlayer formed on the base material, a second interlayer formed on the first interlayer, a third interlayer formed on the second interlayer, and a cubic boron nitride film formed on the third interlayer. Each of the first and second interlayers comprises nitride or boride mixed with an adding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table. In one embodiment of the invention, the composition ratio of the adding element to the nitride or boride decreases towards the surface between the second interlayer and the third interlayer. The third interlayer also contains nitride or boride mixed with an adding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table. In one embodiment of the invention, the total mixing amount of the adding element in the third interlayer is 0.01 atomic % to 10 atomic %, and shows an absorption peak at the wave number of 950 cm -1  to 1150 cm -1  according to infrared absorption spectrum.

This is a division of application No. 07/173,663, filed Mar. 25,1988,now U.S. Pat. No. 4,892,791.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a body coated with cubic boron nitride, and amethod for manufacturing the same.

2. Description of the Prior Art

Recently a film-making technique has been remarkably developed. Variouscoating techniques of the cubic boron nitride have been developed forcoating a part, a tool or the like which requires corrosion-resistance,wear-resistance and high hardness.

Methods disclosed in the Japanese Patent Opening Gazettes Nos.204370/1986, 47472/1987 and 77454/1987 are given as examples for thecoating techniques.

In the method disclosed in the Japanese Patent Opening Gazette No.204370/1986, prasma abundant in electrons is produced by hollow cathodedischarge, and a part of the electrons are attracted towards a reactiongas inlet. Gas is activated, and so reactivity for physical vapourdeposition has been improved.

In the method disclosed in the Japanese Patent Opening Gazette No.47472/1987, a DC or AC bias voltage is applied to a reaction gasintroducing nozzle which is called "activation nozzle", so that plasmais produced with high density. Ions are injected to a body to be coated,from the plasma of high density. Radio frequency (rf) bias voltage isapplied to the body to be coated. Thus, a cubic boron nitride film isformed on the body.

In the Japanese Patent Opening Gazette No. 77454/1987, such a method forforming a cubic boron nitride film is disclosed that a DC or AC biasvoltage is applied to the activation nozzle to produce a plasma of highdensity, a rf bias voltage is applied to a body to be coated, and areaction gas such as Nitrogen gas or hydronitrogen gas and a dischargebase gas such as Argon are mixed and introduced into the vacuum chamberthrough the activation nozzle, or concurrently introduced thereinto.

In both of the above described second method (Japanese Patent OpeningGazette No. 47472/1987) and third method (Japanese Patent OpeningGazette No. 77454/1987), the bias voltage is applied to the gasintroducing nozzle so that plasma of high density is produced adjacentto the opened portion of the gas introducing nozzle, while the rf biasvoltage is applied to the body to be coated, and ions are injected intothe body from the plasma of high density so as to form a cubicboron-nitride film on the body.

Besides the above-described methods, a sputtering method, an ion-beamdeposition method and an ion plating method are well known for forming acubic boron nitride film.

The X-ray diffraction method is used for judging the structure of thefilm. It was reported that the cubic boron nitride film was judged to beformed by the fact that only one peak was obtained nearly at thediffraction angle 2θ=43°within the range of 20° to 50° as shown in FIG.1.

However, the structure of the boron nitride film which was judged to becubic-crystalline by the fact that the maximum peak was obtained nearlyat the diffraction angle 2θ= 43° according to the X-ray diffractionmethod, is classified into two kinds according to the infraredabsorption spectrum method. One of the two kinds shows the absorptionpeaks at the wave numbers of about 1400cm⁻¹ and 800cm⁻¹ , as shown inFIG. 2. The other of the two kinds shows the absorption peak at the wavenumber of about 1050 cm⁻¹. The Vickers hardness of the film of thelatter characteristic is 5000 to 6000 kg/mm². The base material coatedwith such a film, which requires high wear resistance and high hardness,can have a further longer life.

Hitherto, the boron nitride films which were judged to becubic-crystalline by the X-ray diffraction method, show the absorptionpeaks at the wave numbers of about 1400 cm⁻¹ and 800cm⁻¹ according tothe measurement of the X-ray absorption spectrum. Their Vickers hardnessis 2000 to 4000 kg/cm². Accordingly, it is considered that they includeessentially graphite structure (hexagonal boron nitride). They cannot bejudged to be cubic-crystalline from the measurement results of theinfrared absorption spectrum.

On the other hand, the boron nitride film formed by the method disclosedin the Japanese Patent Opening Gazette No. 47472/1987 or 77454/1987 wasconfirmed to be cubic-crystalline both by the X-ray diffractionmeasurement and infrared absorption spectrum method.

However, the film of a few hundreds A thick near the surface boundaryhas graphite structure (h-BN film) which shows the absorption peaks atthe wave-numbers of about 1400 cm⁻¹ and 800cm⁻¹ according to theinfrared absorption spectrum measurement, even in the base materialcoated with the cubic boron nitride film which shows the absorption peakat the wave number of about 1050cm⁻¹. The surface boundary between thebase material and the film is instable to moisture in the atmosphere.Adherence strength between them is essentially low. Accordingly, whenthe base material coated with such a film is let alone in theatmosphere, it has been found that the film is easily peeled from thebase material due to the internal stress of the film.

On the other hand, the boron nitride film containing excess boron(B/N>1) has graphite structure according to the infrared absorptionspectrum measurement. However, the film strength can be improved, sinceB--B bonds exist therein. When such a film containing excess boron isinterposed as an interlayer between the cubic boron-nitride film and thebase material, the adhering strength of the film can be improved.However, when the thickness of the cubic boron nitride film is increasedfor a practical use, the peeling occurs at the surface boundary betweenthe boron nitride film containing excess boron, and the cubic boronnitride film. Accordingly, it cannot be practically used.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide a body coatedwith cubic boron nitride film in which the film strength can be improvedand so stable in the atmosphere that the adherence strength can beimproved, and to provide a method for manufacturing such a body coatedwith cubic boron nitride film.

In accordance with an aspect of this invention, a body coated with cubicboron nitride comprising: (A) a base material; (B) a first interlayer ofnitride or boride mixed with at least one adding element of IVb group,IIIb group, Vb group, IVa group, Va group and VIa group of the periodictable, and the composition ratio of said at least one adding element isdecreased towards the surface, said first interlayer being formed onsaid base material; and/or a second interlayer of nitride or boridemixed with at least one element of IVb group, IIIb group, Vb group, IVagroup, Va group and VIa group of the periodic table, the total mixingamount of the adding element being 0.01 atomic % to 10 atomic %, andshows an absorption peak at the wave number of 950cm⁻¹ to 1150cm⁻¹according to the infrared absorption spectrum, said second interlayerbeing formed on said first interlayer or said base material; and (C) acubic boron nitride film which shows the maximum absorption peak at thewave number of 950 cm⁻¹ to 1150⁻¹ according to the infrared absorptionspectrum, said cubic boron nitride film being formed on said firstinterlayer or said second interlayer.

In accordance with another aspect of this invention, a body coated withcubic boron nitride comprising; (A) a base material, (B) a firstinterlayer of nitride or boride which contains at least one addingelement of IVb group, IIIb group, Vb group, IVa group, Va group and VIagroup of the periodic table, said first interlayer being formed on saidbase material; (C) a second interlayer of nitride or boride mixed withat least one adding element of IVb group, IIIb group, Vb group, IVagroup, Va group and VIa group of the periodic table, and the compositionratio of said adding element is decreased towards the surface, saidsecond interlayer being formed on said first interlayer, (D) a thirdinterlayer of nitride or boride mixed with at least one adding elementof IVb group, IIIb group, Vb group, IVa group, Va group and VIa group ofthe periodic table, the total mixing amount of said adding element being0.01 atomic % to 10 atomic %, and shows an absorption peak at the wavenumber of 950cm⁻¹ to 1150cm⁻¹ according to the infrared absorptionspectrum, said this interlayer being formed on said second interlayerand (E) a cubic boron nitride film which shows the maximum absorptionpeak at the wave number of 950cm⁻¹ to 1150cm⁻¹ according to the infraredabsorption spectrum, said cubic boron nitride film being formed on saidthird interlayer.

In accordance with a further aspect of this invention, a method, formanufacturing a body coated with cubic boron nitride comprising thesteps: (A) of preparing a base material in a vacuum chamber, (B) ofpreparing at least one element of IVb group, IIIb group, Vb group, IVagroup, Va group and VIa group of the periodic table, being able to forma compound with boron and nitrogen, or said compound of said at leastone element; (C) of introducing said elements or compound into saidvacuum chamber under the control of the evaporation rate or supply speedof said elements or compound, and concurrently under the control of theevaporation rate of boron; and (D) of forming an interlayer of nitrideor boride having a predetermined chemical composition between said basematerial and a cubic boron nitride film.

The foregoing and other objects, features, and advantages of the presentinvention will be more readily understood upon consideration of thefollowing detailed description of the preferred embodiments of theinvention, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THF DRAWINGS

FIG. 1 is graph showing the results of the X-ray diffraction measurementof the boron nitride film produced by the prior method;

FIG. 2 is a graph showing the results of the infrared absorptionspectrum measurement of the boron nitride film produced by the priormethod.

FIG. 3 is a graph showing the infrared absorption spectrum of the cubicboron nitride film;

FIG. 4 is an enlarged view of a part of a body coated with cubic boronnitride according to this invention;

FIG. 5 is a graph showing an example of composition of an interlayeraccording to this invention;

FIG. 6 is a graph for explaining the method of this invention.

FIG. 7 is a schematic view of an apparatus for forming the filmaccording to this invention; and

FIG. 8 is a graph showing another example of composition interlayeraccording to this invention.

DESCRIPTION OF THF PREFERRED EMBODIMENTS

FIG. 4 shows the structure of the body coated with cubic boron nitrideaccording to this invention. In FIG. 4, a base material 1 is made of,for example, silicon, WC (tungsten carbide) or Al₂ O₃. An interlayer 2which contains at least one element of IVb group, IIIb group, Vb group,IVa group, Va group and VIa group being able to form compounds withboron and nitrogen, is formed on the base material 1. A cubic boronnitride film or layer 3 is formed on the interlayer 2. The interlayer 2and the cubic boron nitride film 3 are formed by the apparatus shown inFIG. 7 which is partially shown in the Japanese Patent Opening gazetteNos. 47472/1987 and 77454/1987. Next, the apparatus of FIG. 7 will bedescribed. A first evaporation source 12 containing silicon, and asecond evaporation source 13 containing boron are arranged in a vacuumchamber 11. Electron beams EB as shown by dash-lines, heat and evaporatesilicon and boron in the sources 12 and 13. A partition wall 14 isarranged between the sources 12 and 13. Shutters 21 and 22 are arrangedin face to the sources 12 and 13. A substrate or base material 18 to becoated is put directly over the sources 12 and 13. A shutter 20 isarranged under the substrate 18.

A thermal emitter 23 which consists of W(tungsten) filament, is arrangedadjacent to the one side wall of the vacuum tank 11. An alternatecurrent source 24 is connected through a transformer 25 to the thermalemitter 23. A rf power source 29 is connected through a matchingcircuit, which consists of capacitors and an inductance coil, to thesubstrate 18. A halogen lamp 19 for heating the substrate 18 is arrangedabove the substrate 18.

An activation nozzle 15 is fixed at the other side wall. Argon gas andnitrogen gas are supplied through a valve 16 into the activation nozzle15. They are mixed and introduced into the vacuum tank 11 from theactivation nozzle 15. Or they are concurrently introduced from theactivation nozzle 15. A direct current source 26 is connected to theactivation nozzle 15, and it is connected to the transformer 25. Anexhausting opening 17 is made at the other side wall, and it isconnected to not-shown trap and diffusion pump.

Quartz oscillator thickness monitors 27 and 28 are arranged at bothsides of the substrate 18. Evaporation rates of silicon and boron fromthe sources 12 and 13 are measured by the monitors 27 and 28,respectively. Although not shown, output terminals of the monitors 27and 28 are connected to the sources 12 and 13. A feed-back control iseffected for obtaining predetermined evaporation speeds. FIG. 5 showsone example of the interlayer 2 obtained by the apparatus of FIG. 7, inwhich silicon (Si) is used as an adding element. A layer (A) mostadjacent to the base material 1 consists of nitride of Si₃ N₄, and it is0.3 μm thick. The compositions of layers (B) and (C) change from Si₃ N₄to BN through B×SiyNz (as Si₃ N₄ →B×SiyN₂ →BN), where x,y and zrepresent mixing ratio of elements B. Si and N. respectively. Thecomposition ratios of the adding element (Si) are decreased towards thesurface in the interlayers (B) and (C). The decreasing gradient of thelayer (C) is smaller than that of the layer (B). The composition ofnitrogen (N) is omitted in FIG. 5.

FIG. 6 shows a parameter region in which the cubic boron film is formedaccording to this invention in use of the methods disclosed in theJapanese Patent Opening Gazette Nos. 47472/1987 and 77454/1987, or theapparatus of FIG. 7. As understood from FIG 6, the cubic boron nitridecan be formed in the range over the thresholds of the RF power andactivation nozzle current. The RF power is applied as a bias voltage tothe base material 1.

FIG 8 shows another example of the interlayer 2 obtained by theapparatus of FIG. 7 in which silicon (Si) is similarly used as an addingelement. In FIG. 8, the evaporation rate of the Si evaporation source isconstant in the layer (A') which consists of silicon nitride and is 0.2μm thick. For the layer (B'), the heating of the boron evaporationsource starts, while the evaporation rate of the Si evaporation sourceis reduced. The decreasing gradient of Si and the increasing gradient ofboron are predetermined in FIG. 8. The layer (B') contains the mixtureof silicon nitride and boron nitride, and it is 0.2 μm thick. In thelayer (C'), the decreasing gradient of Si evaporation becomes smallerthan in the layer (B'), while the increasing gradient of boronevaporation becomes smaller than in the layer (B'). The table I showsthe measurement results on the adherence strengths of the cubic boronnitride (C--BN) films in the atmosphere, in comparison with the priorart method. The cubic boron nitride films are formed through theinterlayers 2 on the Si-substrate or WC-Co tip, respectively, at thedifferent thicknesses. The interlayers 2 have the structure shown inFIG. 5.

                  TABLE I                                                         ______________________________________                                                     C--BN film thick                                                 Film Construction                                                                            0.5 μm   1 μm                                                                              3 μm                                     ______________________________________                                        C--BN/Interlayer/Si                                                                          ∘                                                                             ∘                                                                        ∘                               C--BN/Interlayer/                                                                            ∘                                                                             ∘                                                                        ∘                               WC--Co tip                                                                    Prior Art      x           x      x                                           ______________________________________                                    

In the Table I, the mark ◯ represents good adherence, while the mark xrepresents bad adherence. In the prior art, the films were peeled in avery short time, in the atmosphere. The measurements were made on whatelement was effective for improving the adherence strength of the filmbesides silicon, as the adding element. Table II shows the measurementresults of the cubic boron nitride films on the different addingelements. The thickness of the interlayer is constant and 2000 Å, inwhich the composition ratio of the adding element is decreased from thebase material (Si) towards the cubic boron nitride film.

                  TABLE II                                                        ______________________________________                                               Adding element to Interlayer                                           C--BN film                                                                             Ib group IIb group IIIb group                                                                            IVb group                                 thick    Cu       Zn        Al      C   Si   Ge                               ______________________________________                                        0.1 μm                                                                              x        x         ∘                                                                         ∘                                                                     ∘                                                                      ∘                    0.3 μm                                                                              x        x         ∘                                                                         ∘                                                                     ∘                                                                      Δ                          ______________________________________                                               Adding element to Interlayer                                                    Vb       IVa      Va    VIa    VIIIa                                 C--BN film                                                                             group    group    group group  group                                 thick    P        Ti       Nb    Cr     Ni                                    ______________________________________                                        0.1 μm                                                                              ∘                                                                          ∘                                                                          ∘                                                                       ∘                                                                        x                                     0.3 μm                                                                              Δ  ∘                                                                          Δ                                                                             Δ                                                                              x                                     ______________________________________                                         In the Table II, the mark ◯ represents good adherence, the     mark Δ considerable bad adherence and the mark x bad adherence. In     the mark Δ, the film is partially peeled in a very short time under     the atmosphere. In the mark x, the film is entirely peeled in a very short     time under the atmosphere.

It is confirmed from the table II that the elements of IIIb group, IVbgroup, Vb group, IVa group, Va group and VIa group of the periodic tableare effective for improving the adherence strength of the film.

Table III shows the experimental results of the adherences on thedifferent structures of the interlayers.

                                      TABLE III                                   __________________________________________________________________________                      WC base  Al.sub.2 O.sub.3 base                              Base material                                                                        Si wafer   tip      tip                                                __________________________________________________________________________    Structure of                                                                         B C C/B                                                                              C/B/A                                                                             B C/B                                                                              C/B/A                                                                             B C/B                                                                              C/B/A                                                                             C                                         Interlayer                                                                    Adherence                                                                            Δ                                                                         ∘                                                                   ∘                                                                    ∘                                                                     Δ                                                                         Δ                                                                          ∘                                                                     Δ                                                                         ∘                                                                    ∘                                                                     Δ                                   __________________________________________________________________________

In the Table III, the meanings of the marks ◯ and Δ are equal to thosein the Table II. The meanings of the layers A, B and C are equal tothose of the layers (A) (B) and (C) in FIG. 5, respectively. B and Crepresent the single layer structure of (B) and (C), respectively. C/Brepresents that the layer (B) is formed on the base material, and thelayer (C) is formed on the layer (B). C/B/A is equal to the structure(A) (B) (C) shown in FIG. 5. The thicknesses of the interlayers A, B andC are 2000Å, respectively. The thickness of the cubic-crystalline filmis 1 μm. The element Si was used as the adding element.

Generally defined, the interlayer A is equal to the nitride layer orboride layer which contains at least one kind of element of the IVbgroup, IIIb group, Vb group, IVa group, Va group and VIa group of theperiodic table. The interlayer B is equal to the nitride layer or boridelayer with which at least one kind of element of the IVb group, IIIbgroup, Vb group, IVa group, Va group and VIa group of the periodictable, is mixed and in which the composition ratio of said at least onekind of element is decreased from the base material towards the surface.And the interlayer C is equal to the nitride layer or boride layer withwhich at least one element of the IVb group, IIIb group, Vb group, IVagroup, Va group and VIa group of the periodic table, is mixed at thetotal mixture amount of 0.01 atomic % to 10 atomic %, and which has theabsorption peak at the wave number of 950 cm⁻¹ to 1150 cm⁻¹.

As understood from the table III, the good adherence can be obtained bythe suitable selection of the interlayer structure in accordance withthe kind of the base material. As above described, according to thisinvention, at least one element of the IVb group, IIIb group Vb group,IVa group, Va group and VIa group of the periodic table, is added toform the three-dimensional bonds in the graphite structure of thesurface boundary. Thus, even when the base material is coated with athick cubic boron nitride film, this film can resist sufficiently theinternal stress, and the adherence can be greatly improved. Accordingly,this invention is very useful for parts or tools which requirecorrosion-resistance, wear-resistance and high hardness.

While the preferred embodiment has been described, variations theretowill occur to those skilled in the art within the scope of the presentinventive concepts which are delineated by the following claims.

What is claimed is:
 1. A body coated with cubic boron nitridecomprising:(A) a base material; (B) a first interlayer formed on saidbase material wherein said first interlayer comprises nitride or boride,the nitride or boride comprising nitrogen or boron elements with anadding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups ofthe periodic table; (C) a second interlayer formed on said firstinterlayer wherein said second interlayer comprises nitride and boride,the nitride and boride comprising nitrogen and boron elements with anadding element chosen from the IVb, IIIb, Vb, IVa, Va and VIa groups ofthe periodic table, and further wherein the composition ratio of saidadding element of the boride and nitride decreases towards the surfacebetween a second interlayer and said third interlayer; (D) a thirdinterlayer formed on said second interlayer wherein said thirdinterlayer comprises nitride and boride, the nitride and boridecomprising nitrogen and boron elements with an adding element chosenfrom the IVb, IIIb, Vb, IVa, Va and VIa groups of the periodic table,and further wherein the total mixing amount of the adding element is0.01 atomic % to 10 atomic %, and further wherein said third interlayershows an absorption peak at the wave number of 950cm⁻¹ to 1150cm⁻¹according to the infrared absorption spectrum; (E) a cubic boron nitridefilm formed on said third interlayer wherein said cubic boron nitridefilm shows a maximum absorption peak at the wave number of 950cm⁻¹ to1150cm⁻¹ according to the infrared absorption spectrum.
 2. A bodyaccording to claim 1 wherein said adding element of said thirdinterlayer has a composition ratio which decreases towards the surfacebetween said third interlayer and said cubic boron nitride film.
 3. Abody according to claim 2 wherein the decreasing gradient of thecomposition ratio of said adding element in said second interlayer islarger than that in said third interlayer.
 4. A body according to claim1 wherein the ratio of boron elements to nitrogen elements is increasedtowards the surface between said second interlayer and said thirdinterlayer in said second interlayer.
 5. A body according to claim 4wherein the ratio of boron elements to nitrogen elements is increasedtowards the surface between said third interlayer and said cubic boronnitride film in said third interlayer.
 6. A body according to claim 5wherein the increasing gradient of said ratio in said second interlayeris larger than that in said third interlayer.
 7. A body according toclaim 1 wherein the thickness of each of said first, second and thirdlayers is on the order of 0.2μm.
 8. A body according to claim 1 whereinthe ratio of nitrogen elements to boron elements is increased towardsthe surface between said second interlayer and said third interlayer insaid second interlayer.
 9. A body according to claim 8 wherein the ratioof nitrogen elements to boron elements is increased towards the surfacebetween said third interlayer and said cubic boron nitride film in saidthird interlayer.
 10. A body according to claim 9 wherein the increasinggradient of said ratio in said second interlayer is larger than that insaid third interlayer.
 11. A body according to claim 1 wherein thethickness of the cubic boron nitride film is from 0.01μm to 3μm.